A pulse start method and a pulse start device for an internal combustion engine are described in German Patent Application No. DE 103 56 384 C1. According to the pulse start method described in German Patent Application No. DE 103 56 384 C1, during a wind-up phase, a flywheel is accelerated in rotary drive and subsequently, during a coupling phase, the rotating flywheel is coupled to a rotatably supported shaft, preferably the crankshaft of the internal combustion engine, for the transmission of torque. During the wind-up phase and/or the coupling phase, the speed pattern of the flywheel is evaluated, and it is derived from this evaluation whether a successful start of the internal combustion engine is possible. If a successful start of the internal combustion engine is not to be expected, the internal combustion engine is brought via the shaft to an operating position favorable for a subsequent second starting attempt. According to the pulse start method described in German Patent Application No. DE 103 56 384 C1, during the wind-up phase, the gradient of the speed pattern of the flywheel is used for the evaluation, and if the gradient is too low, the coupling phase is initiated. Hybrid drives for motor vehicles generally include an internal combustion engine and at least one additional drive, as for instance at least one electric drive. Using vehicles equipped with a hybrid drive, one may implement a purely electrical driving operation. If the electrical energy or the power output of the battery included in the traction network of the hybrid drive gets close to its limits, the internal combustion engine is switched on. For this purpose, it is started and a separating clutch separating the internal combustion engine from at least one electric drive should be closed. In conventional design approaches, the internal combustion engine is suddenly pulled on by the closing of the clutch. A special clutch is frequently used for this purpose, that is designed for a correspondingly high energy input. The energy required for starting the internal combustion engine of the hybrid drive is established by the magnitude of the internal combustion engine drag torque and the difference in rotational speed between the stationary internal combustion engine and the at least one electric drive that is in rotation, as well as the duration of the starting process for starting the internal combustion engine. The pulling on of the internal combustion engine using the above-mentioned clutch generally leads to a negative influence on the traction, that is, the propulsion of the vehicle, since the power required for starting the internal combustion engine is at the expense of the propulsion. Furthermore, the torque pattern in the drive train of a vehicle having hybrid drive, during this process, namely the direct start of the internal combustion engine from the purely electrical driving operation, may be interfered with by vibrations or excess torque. These interferences may not be compensated for at all, in part, or compensated for only with great effort, and in this connection, drive types having constant power transmission to the driving wheels, such as classical automatic transmissions having torque converters, are especially affected by the loss of comfort.
One possibility for a remedy is starting the internal combustion engine of a hybrid drive using a separate starter. The disadvantages that go along with this design approach are in the higher costs for the starter as well as the typical noise during the external start, which originates from the engaging of the starter and the engine compression before the first combustion stroke.
In hybrid drive vehicles, the demand for a noise-free transition from the purely electrical driving operation to the hybrid operation is particularly great since the purely electrical driving operation essentially proceeds without noise, and criteria have been set very high by existing mass-produced vehicles having hybrid drive.